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Abstract:

An electromagnetic and/or chemical enhancement which greatly enhances the
Raman signal response for Surface Enhanced Raman is directed to molecular
probe systems. Such molecular probe systems have many properties that
make them ideal as probes for Scanning Probe Microscopy, Atomic Force
Microscopy, and many other applications.

Claims:

1. A process for fabricating a carbon nanotube (CNT) device, the process
comprising: applying a material to the CNT device enabling an enhanced
Raman signal.

2. The process of claim 1, wherein the CNT device is created using Ion
Flux Molding (IFM).

3. The process of claim 1, wherein the material is formed using one or
more of: a second thermal chemical vapor deposition (CVD) process; a
physical vapor deposition process; a CVD process; a plasma-enhanced CVD
process; an electrochemical deposition process; a molecular beam epitaxy
process; an electrochemical deposition process; a spin casting process;
an evaporation process; a reactive growth process; or an atomic layer
deposition process.

4. The process of claim 1, wherein the material is one or more of: a
silicon dioxide (SiO2) surface; a doped silicon surface; a compound
silicon surface; a polymer surface; or a lithographic resist surface.

5. The process of claim 1, wherein an intermediate layer is applied to
improve adhesion of the material to the CNT.

6. The process of claim 1, wherein the material includes an insulating
material.

7. The process of claim 1, wherein the material includes a semiconducting
material.

8. The process of claim 1, wherein the material includes a conductive
material.

9. The process of claim 1, wherein the material includes at least one of
the following: silver; gold; platinum; copper; or rhodium.

10. The process of claim 1, wherein a property relating to the material
can vary.

11. The process of claim 10, wherein the property is at least one of the
following: material property; dielectric environment; thickness; volume;
arrangement; size; dimensions; aspect ratio; or shape.

19. The process of claim 1, wherein the CNT device is fabricated from
silicon, silicon nitride, or silicon dioxide using lithographic
processing.

20. The process of claim 1, wherein the CNT device has been modified by
chemical reaction, material adherence decoration, or immersion of
reactive or non-reactive species, for enhancement of probing interaction
of other purpose.

21. The process of claim 1, wherein the CNT device is a single walled
structure grown using a thermal chemical vapor deposition process.

22. The process of claim 1, wherein the CNT device is a multi-walled
structure grown using a thermal chemical vapor deposition process.

23. The process of claim 1, wherein the CNT device is used in at least
one of: an atomic force microscope (AFM); or a scanning probe microscope
(SPM).

24. The process of claim 1, wherein the CNT device is an array of probes.

25. The process of claim 9, wherein the CNT device is an array of probes.

26. The process of claim 24, wherein a length of the CNT device is
exposed, wherein said exposed length being defined by a specific
application for said CNT device.

27. The process of claim 1, wherein the CNT device is suitable for use in
at least one of: a field emitter; a sensor; a lithographic device; a
logic device; an electrical contact; or an electrical interconnect.

28. The process of claim 24, wherein the CNT device is used in at least
one of: scanning probe microscope (SPM).

29. The process of claim 24, wherein the CNT device is suitable for use
in at least one of: a nanotube based antenna device; nanotube tweezers; a
nanotube based manipulator device; a nanotube based actuator; or a
nanotube based lever arm.

30. The process of claim 24, wherein the CNT device is suitable for use
in at least one of: a field emitter; a sensor; a lithographic device; a
logic device; an electrical contact; or an electrical interconnect.

31. A device comprising: a carbon nanotube (CNT) which is a base of a
nanostructure, wherein the nanostructure is comprised of more than one
material.

32. The device of claim 31, wherein the CNT is created using Ion Flux
Molding (IFM).

33. The device of claim 31, wherein the more than one material is formed
using one or more of: a second thermal chemical vapor deposition (CVD)
process; a physical vapor deposition process a CVD process; a CVD
process; a plasma-enhanced CVD process; an electrochemical deposition
process a spin casting process; an evaporation process; reactive growth
process; or an atomic layer deposition process.

34. The device of claim 31, wherein the more than one material includes
one or more of: an silicon dioxide (SiO2) surface; a doped silicon
surface; a compound silicon surface; a polymer surface; or a lithographic
resist surface.

35. The device of claim 31, wherein the more than one material is a
material which increases adhesion to the CNT base or between layers.

36. The device of claim 31, wherein the more than one material includes
an insulating material.

37. The device of claim 31, wherein the more than one material includes a
semiconducting material.

38. The device of claim 31, wherein the more than one material includes a
conductive material.

39. The device of claim 31, wherein the more than one material includes
at least one of the following: silver; gold; platinum; copper; or
rhodium.

40. The device of claim 31, wherein a property relating to the more than
one material can vary.

41. The device of claim 40, wherein the property is at least one of the
following: material property; dielectric environment; thickness; volume;
arrangement; size; dimensions; aspect ratio; or shape.

48. The device of claim 31, wherein the CNT is a carbon nanofiber
structure grown using a plasma enhanced chemical vapor deposition
process.

49. The device of claim 31, wherein the device is fabricated from
silicon, silicon nitride, or silicon dioxide using lithographic
processing.

50. The device of claim 31, wherein the CNT has been modified by chemical
reaction, material adherence decoration, or immersion of reactive or
non-reactive species, for enhancement of probing interaction of other
purpose.

51. The device of claim 31, wherein the CNT is a single walled structure
grown using a thermal chemical vapor deposition process.

52. The device of claim 31, wherein the CNT is a multi-walled structure
grown using a thermal checmical vapor dposition process.

53. The device of claim 31, wherein the CNT is used in at least one of:
an atomic force microscope (AFM); or a scanning probe microscope (SPM).

54. The device of claim 31, wherein the CNT is an array of probes.

55. The device of claim 39, wherein the CNT is an array of probes.

56. The device of claim 54, wherein a length of the CNT is exposed,
wherein said exposed length being defined by a specific application for
said CNT device.

57. The device of claim 54, wherein the device is suitable for use in at
least one of: a field emitter; a sensor; a lithographic device; a logic
device; an electrical contact; or an electrical interconnect.

58. The device of claim 54, wherein the CNT is used in at least one of:
an atomic force microscope (AFM); or a scanning probe microscope (SPM).

59. The device of claim 31, wherein the CNT is suitable for use in at
least one of: a nanotube based antenna device; nanotube tweezers; a
nanotube based manipulator device; a nanotube based actuator; or a
nanotube based lever arm.

60. The device of claim 31, wherein the CNT is suitable for use in at
least one of: a field emitter; a sensor; a lithographic device; a logic
device; an electrical contact; or an electrical interconnect.

61. A method comprising: fabricating a molecular sensor probe for an
enhanced Raman signal, wherein the sensor probe is comprised of more than
one material.

62. The method of claim 61, wherein the molecular sensor probe is created
using Ion Flux Molding (IFM).

63. The method of claim 61, wherein the more than one material: is grown;
is layered; is deposited; or is coupled to the CNT base.

64. The method of claim 61, wherein the more than one material includes a
polymer.

65. The method of claim 61, wherein the more than one material includes
silicon dioxide.

66. The method of claim 61, wherein an intermediate material improves
adhesion of the more than one material to the CNT.

67. The method of claim 61, wherein the more than one material includes
an insulating material.

68. The method of claim 61, wherein the more than one material includes a
semiconducting material.

69. The method of claim 61, wherein the more than one material includes a
conductive material.

70. The device of claim 61, wherein more than one material includes at
least one of the following: silver; gold; platinum; copper; or rhodium.

71. The method of claim 61, wherein a property relating to the more than
one material can vary.

72. The method of claim 71, wherein the property is at least one of the
following: material property; dielectric environment; thickness; volume;
arrangement; size; dimensions; aspect ratio; or shape.

81. The method of claim 61, wherein the molecular sensor probe is
fabricated from silicon, silicon nitride, or silicon dioxide using
lithographic processing.

82. The method of claim 61, wherein the molecular sensor probe has been
modified by chemical reaction, material adherence decoration, or
immersion of reactive or non-reactive species, for enhancement of probing
interaction of other purpose.

83. The method of claim 61, wherein the molecular sensor probe is a
single walled structure grown using a thermal chemical vapor deposition
process.

84. The method of claim 61, wherein the molecular sensor probe is a
multi-walled structure grown using a thermal chemical vapor deposition
process.

85. The method of claim 61, herein the molecular sensor probe is used in
at least one of: an atomic force microscope (AFM); or a scanning probe
microscope (SPM).

86. The method of claim 61, wherein the molecular sensor probe is an
array of probes.

87. The method of claim 70 wherein the molecular sensor probe is an array
of probes.

88. The method of claim 61, wherein a length of the molecular sensor
probe is exposed, wherein said exposed length being defined by a specific
application for said molecular sensor probe.

89. The method of claim 61, wherein the molecular sensor probe is
suitable for use in at least one of: a field emitter; a sensor; a
lithographic device; a logic device; an electrical contact; or an
electrical interconnect.

90. The method of claim 86, wherein the molecular sensor probe is used in
at least one of: an atomic force microscope (AFM); or a scanning probe
microscope (SPM).

91. The method of claim 86, wherein the molecular sensor probe is
suitable for use in at least one of: a nanotube based antenna device;
nanotube tweezers; a nanotube based manipulator device; a nanotube based
actuator; or a nanotube based lever arm.

92. The method of claim 86, wherein the molecular sensor probe is
suitable for use in at least one of: a field emitter; a sensor; a
lithographic device; a logic device; an electrical contact; or an
electrical interconnect.

[0003] The present invention relates to molecular probing, sensing and
surface modification devices and systems and in particular without
limitation relates to techniques that improve the Raman signal response
for Surface Enhanced Raman.

SUMMARY OF THE DESCRIPTION

[0004] Disclosed are techniques for fabrication and testing of a carbon
nanotube (CNT)-based nano-electronic probe substrate for Surface Enhanced
Raman Scattering (SERS) for molecular sensing and material modification
applications. In some embodiments, the molecular probe system begins with
an as-made CNT that is straightened or re-shaped and precision aligned
along a desired axis. This probe is then transformed into a metal-coated
(e.g., silver (Ag), gold (Au), platinum (Pt)), nano-engineered probe for
maximized probe-molecule interaction. The probe can be further combined
with scanning-probe microscopy, electrochemical, spectro-chemical, or
other analytical methods for improving the analytical power of the
approach. The technique utilizes high aspect ratio CNTs coated with
dipole coupling metals with precise size and shape control for optimizing
electric-field coupling for maximum SERS, near-field, and fluorescence
response at nanoscale sites.

[0005] Other advantages and features will become apparent from the
following description and claims. It should be understood that the
description and specific examples are intended for purposes of
illustration only and not intended to limit the scope of the present
disclosure.

BRIEF DESCRIPTION OF DRAWINGS

[0006] These and other objects, features and characteristics of the
present invention will become more apparent to those skilled in the art
from a study of the following detailed description in conjunction with
the appended claims and drawings, all of which form a part of this
specification. In the drawings:

[0013] Various examples of the invention will now be described. The
following description provides specific details for a thorough
understanding and enabling description of these examples. One skilled in
the relevant art will understand, however, that the invention may be
practiced without many of these details. Likewise, one skilled in the
relevant art will also understand that the invention can include many
other obvious features not described in detail herein. Additionally, some
well-known structures or functions may not be shown or described in
detail below, so as to avoid unnecessarily obscuring the relevant
description.

[0014] The terminology used below is to be interpreted in its broadest
reasonable manner, even though it is being used in conjunction with a
detailed description of certain specific examples of the invention.
Indeed, certain terms may even be emphasized below; however, any
terminology intended to be interpreted in any restricted manner will be
overtly and specifically defined as such in this Detailed Description
section.

[0015] The techniques described herein generally entail employing carbon
nanotube (CNT) nanomanufacturing techniques to fabricate a CNT-based
enhanced Raman spectroscopy molecular sensor probe and molecular
detection system. Several suitable CNT nanomanufacturing techniques are
described in detail in U.S. Pat. No. 7,628,972, issued on Dec. 8, 2009,
entitled "NANOSTRUCTURE DEVICES AND FABRICATION METHOD", U.S. patent
application No. 12/606,143, filed Oct. 26, 2009, entitled " NANOSTRUCTURE
DEVICES AND FABRICATION METHOD", U.S. Pat. No. 7,601,650, issued on Oct.
13, 2009, entitled "CARBON NANOTUBE DEVICE AND PROCESS FOR MANUFACTURING
SAME", U.S. patent application No. 12/548,400, filed Aug. 26, 2009,
entitled "CARBON NANOTUBE DEVICE AND PROCESS FOR MANUFACTURING SAME",
U.S. patent application No. 11/786,492, filed Apr. 11, 2007, entitled
"CARBON NANOTUBE SIGNAL MODULATOR AND PHOTONIC TRANSMISSION DEVICE" which
are all incorporated by reference in their entireties. According to one
embodiment, the molecular probe system starts with a reshaped
(straightened and aligned) CNT-base probe structure that is then
transformed into a silver (Ag), gold (Au) or platinum (Pt)-coated
nanoengineered composite SERS probe. This probe is the missing element
remaining to establish the more widespread use of the powerful
combination of Scanning Probe Microscopies (SPM) with molecular sensing
spectroscopic methods for improvement of instrumentation for
nanotechnology. Such a probe and probing system represents the use of a
nanoscale CNT material and a nanomanufacturing procedure exemplifying
techniques for the nanomanufacturing of CNTs, and commercial applications
of CNTs resulting in creation of a functional Raman-based molecular
nanosensor probe device. The device uses high aspect ratio CNTs, dipole
coupling materials (e.g., Ag, Au, Pt) polarization effects
(one-dimensional nanoantenna), wavelength coupling length effects with
precise size and shape control incorporated above to optimize enhancement
of the nanoengineered probe structure.

[0016] The nature of the described device and the Coulomb interaction
between valence electrons in metal surfaces yields collective
oscillations called plasmons and aspects of these collective excitations
concentrates light in subwavelength structures. Surface plasmons and
polaritons play a key role in a wide spectrum of science, ranging from
physics and materials science to biology. Collective electronic
excitations at metal surfaces serve as the basis for the design,
fabrication, and characterization of the described device and serves as
the basis for subwavelength waveguide components, plasmonic modulators
and switches, near field microscopy probes, SERS substrates and TERS
probes.

[0017] Surface Enhanced Raman Scattering (SERS) and the related Tip
Enhanced Ramen Spectroscopy (TERS) are becoming increasingly more widely
applicable. SERS as employed in the described device can be applied to
the study of biomolecules and proteins including cancer gene detection,
spectroscopy of living cells and single protein and DNA detection. Some
of the Non-biological applications of the described device include but
are not limited to single molecule detection, spectroscopy of dyes in
nanocrystals and SERS Stokes/anti-Stokes spectroscopy in macromolecules
like carbon nanotubes. SERS is a Raman Spectroscopic (RS) technique,
which under resonant, collective oscillation conditions greatly enhances
the Raman signal from a Raman-active analyte molecule that has been
adsorbed onto a surface. The increased Raman signal is due to surface
effects that lead to the electromagnetic (EM) enhancement and the
chemical enhancement (CE) mechanisms. Increases in the intensity of Raman
signal have been regularly observed on the order of 104-106,
and can be as high as 108 and 1014 for some systems. Raman
Spectroscopy (RS) identifies structural information of an analyte with a
high degree of selectivity.

[0018] The importance of SERS is that it greatly increases sensitivity and
TERS adds localization, extending Raman Spectroscopy (RS) to a wider
variety of interfacial systems including in-situ and ambient analysis of
electrochemical, catalytic, biological, and organic systems. SERS/TERS
can be conducted under ambient conditions not requiring a special
environment. Also, the combination of SERS, which has a broad wave number
range, and a highly selective surface that is highly sensitive, and TERS,
which adds greater localization, creates the potential for direct
molecular identification at the nanometer scale. Greater elucidation of
the SERS phenomena is a result of applicant's extensive experimentation
and theoretical studies of roughened metallic surfaces, metal
nanoparticle and nanorod colloids and other configurations. Additionally,
TERS combines SERS phenomena with Atomic Force Microscopy (AFM) and shows
that similar Raman enhancement can result from a metallized high aspect
ratio probe. There is extensive industry expertise processing silicon and
fabricating silicon AFM cantilever and probe structures, but the
techniques become increasingly more complicated as the structures
approach the nanoscale and limitations in shape and dimension predominate
making CNT-based probes more advantageous. The main challenge that this
innovation overcomes is reproducible mass production of nanoengineered
SERS substrates and TERS probes, probe arrays, and probe tips. This
development is found in the present teaching.

[0019] Improving the mismatch between light and nanoscale objects is
fundamental to the understanding and use of Raman enhancement methods.
However, the CNT processing technology described herein offers advantages
over other potential nanofabrication options by controllably and
reproducibly fabricating Raman-active structures with nanoengineered
signal enhancing properties significantly increasing the advantageous
aspects of the device including the accessibility of ultra sensitive
molecular detection for a wide range of applications.

[0020] Surface Enhanced Raman Scattering (SERS) effect is dependent on the
conductive properties of nanoscale features. Multi-walled carbon
nanotubes (MWCNTs) have been shown to have remarkable material properties
and have dimensions and properties appropriate for electromagnetic
interaction. However, working with CNTs and reliably making commercial
devices from CNTs has proven difficult until Ion Flux Molding (IFM)
processing techniques 10 (described herein and in the cross-referenced
applications indicated above) allowed the CNT to be reformed from its
random native shape 12 and orientation into a straight CNT 14 that is
perfectly set to any angle providing a means to reproducibly make a
nanoscale probe device platform and even probe arrays.

[0021] To this extent, refer to FIG. 1, which illustrates an IFM
processing method 10 for nanoscale control over the morphology of the
CNTs. In accordance to one embodiment, a carbon nanotube 12 having a
curvature and a lack of proper angular alignment can be straightened into
a desired configuration 14 with IFM processing. Through the exposure of
the carbon nanotube to an ion beam, the nanotube probe can be
straightened or bent in the direction from which an ion beam has been
directed.

[0022] Ion Flux Molding (IFM) processing represents a technique for the
fabrication of CNT-based devices by way of controlling the matter of a
CNT at the submicroscopic scale in a systematic and reproducible fashion.
The CNT probe structures described herein comprise an IFM-processed CNT
at the core of a multilayered composite structure that can include
metallized and/or insulated portions. By starting with a CNT at the heart
of the composite probe structure the CNT provides a base scaffold upon
which a more complex composite material may be assembled to match desired
SERS effects. Suitable CNTs include but are not limited to those
providing an approximately 25 nm diameter base nanostructure with lengths
ranging from nanometers to microns and Au, Ag, and Pt coatings of varying
thickness and shape.

[0023] In one embodiment, the probe resulting from the techniques
described herein is an example of the application of an active
nanostructure, combining photonic, chemical, and biological effects to a
wide range of potential commercial products. This also provides the basis
for a SERS/TERS individual "lightning rod" probe in scanning probe
applications or in an array of probes on a substrate and could be applied
to anything from laboratory instrumentation in the life sciences to
handheld detectors and medical diagnostic devices. The single probe
technology described herein can be extended into fabricating arrays of
probes. Probes or arrays of probes can also be used in conjunction with a
Scanning Probe Microscopy (SPM) platform for "hot spot" creation between
the scanning and a second probe or probes. The technology has commercial
applications ranging from water-quality monitoring and medical diagnostic
devices to detection of explosives or chemical warfare agents. The high
aspect ratio of the CNT and the capability to control the material
properties, size and shape of the probe provides for potentially higher
sensitivity, greater specificity and wider applicability and would
represent commercial products based on a high performance, nanoengineered
CNT SERS probe substrate.

[0024] Prior art development of nanoscale materials for Raman enhancement
has been divided into general fields of research: nanoparticle
dispersions and silicon processing of nanoscale structures including AFM
cantilever probes. Chemistry techniques leading to nanoparticle and
nanorod dispersions provide nanoscale control over material properties
but are difficult to control for individual probe fabrication or in
prescribed array spacing and dimensions and cannot be oriented normal to
the surface in a probing configuration reliably. Lithographic processing
of silicon generates a wide range of surface structures but individual
nanoscale high aspect ratio structure fabrication remains a difficult
challenge. Some of the best examples of nanoscale high aspect ratio
structures can be found as AFM probes. Industry leading probe suppliers
offer a wide range of probe types, revealing the potential technological
starting points for development of an individual TERS probe structure.
Standard AFM probes are typically pyramidal in shape and have moderate
aspect ratios. Sharper AFM probes require further processing and are
still only approximately 5:1 aspect ratios.

[0025] Metallized CNT-based nanoantenna structures have the highest aspect
ratios and the potential to optimally provide optical fields that are
confined to spatial scales below the diffraction limit. CNT-based
metallized nanoantennas provide a platform to fabricate optimized Raman
enhancing sensor devices and commercial products that exploit the
interaction between electromagnetic fields and nanoscale objects. CNTs
fabricated into functional antenna forms demonstrate photonic properties
and antenna efficiencies comparable to predicted theoretical values.
Further details of these photonic properties are explained in detail in
U.S. patent application No. 11/786,492, filed Apr. 11, 2007, entitled
"CARBON NANOTUBE SIGNAL MODULATOR AND PHOTONIC TRANSMISSION DEVICE",
which is incorporated in its entirety herein. Measured polarization is
dependent upon the orientation of the CNT and IFM, proved capable of
reproducibly orienting the CNT with precise right angles with length
scales in the visible wavelength range. Additionally, metallized
CNT-based nanostructures have the potential to improve the mismatch
between light and a nanoscale probe or antenna.

[0026] Experimental results show that the local intensity enhancement
factor relative to that for an incident diffraction-limited beam shows a
strong dependence on polarization. Theoretical predictions for TERS
probes define the tip shape, volume, surface material and thickness,
incident beam angle, wavelength and polarization as the dominant factors
affecting enhancement.

[0027] The dominant factors for tip shape are cone angle and tip radius.
Plasmon enhancement of the Raman signal can be as high as 1014 in
particular spots or clusters of Ag particles called "hot spots"
exhibiting a complicated dependence on factors including the size, aspect
ratio, spacing between particles, and clustering effects.

[0028] Electromagnetic enhancement factors for TERS probes have been
reported on the order of 102-104 and precise control of tip
properties may account for some of the difference between SERS and TERS.
In TERS, a tip is used to enhance the Raman signal at a very localized
region of the sample within a larger area that is being illuminated with
laser light. This configuration is similar to a "rough" feature on a bulk
substrate.

[0029] The aspect ratio of SERS/TERS structures plays an important role in
Raman enhancement. Currently there are existing strategies utilizing
colloid nanopartical dispersions or preexisting silicon lithographic
structures that have generated promising data in laboratory settings.
However, the CNT fabrication techniques described herein, combined with
traditional silicon processing, offers a unique opportunity to directly
fabricate a nanoscale probe structure with controlled material properties
onto a desired substrate with the potential for commercial production
volumes. The metallized CNT-based probe structures described herein
created using IFM have an advantage in controllably fabricating high
aspect ratio nanostructures. Controlled probe fabrication can lead to
multiple novel applications such as intracellular single molecule
detection or nanoscale defect analysis in semiconductor metrology and
extrapolation of probe technology to arrays expands applicability
further.

[0030] Almost all Single Molecule Surfaced Enhanced Raman Scattering
(SMSERS) observations with nominal enhancement factors of 1013 or
greater have been with resonant Raman scatterers showing an increased
intensity over nonresonant molecules by a factor of 104. Silver (Ag)
has been widely reported associated with SERS phenomena along with gold
(Au) and copper (Cu) and with evidence observed for platinum (Pt) and
rhodium (Rh) as well. Continuum electrodynamics studies predict the
enhancement factor for a nonresonant molecule on a single silver
nanoparticle, when optimized for size and shape, is approximately
105. Predictions can range as high as Emax=1010-1011
for dimers of silver with nonresonant molecules. Emax values of
109 and even 1013 have been predicted for increasingly more
precisely engineered structures and geometries designed to take advantage
of both the short range interactions associated with a dimer junction
structure and long range electrodynamic interactions.

[0031] The enhancements have been shown to be the result of two separate
phenomena: the electromagnetic (EM) and the chemical enhancement (CE)
mechanisms. The EM enhancement factors cannot be completely extricated
from the CE factors.

[0032] Computational electrodynamics studies of extinction and scattering
spectra show that the EM enhancement factors of metal nanoparticles
depend on their size, shape, arrangement, and dielectric environment, as
shown in the illustration depicted in FIG. 2. FIG. 2 illustrates a chart
20 representing how material properties and shape (e.g.; diameter, aspect
ratio) can affect the local electric field, thereby enhancing the
SERS-response. The y-axis represents the maximum absorption of the
longitudinal Plasmon resonance and the x-axis represents a scale of
increasing aspect ratio. For each corresponding aspect ratio and/or
shape, the datapoint(s) 22 represent estimated corresponding maximum
absorption. In an exemplary embodiment, the maximum absorption of a
nanoparticle enhanced with gold 24 is relatively lower than a nanorod
enhanced with gold 26. As another example, the maximum absorption of a
Au-coated Silicon AFM probe 28 is lower than a Au-coated Multi-Walled CNT
30. As such, the FIG. 2 depicts an estimated dependence of the
SERS-enhancement on the aspect ratio of the nanoscope.

[0033] SERS studies using colloidal aggregates of nanoparticles and
nanorods can be compared with TERS applications and Atomic Force
Microscopy (AFM)-probe based enhancements, revealing that for a given
metal, polarization, wavelength, incident angle, and target molecule;
aspect ratio, size, and shape become the dominant factors. Polarization,
wavelength, and incident angle are determined instrumentally and
therefore precise control over the aspect ratio, size, and shape of
nanoscale metallized nanostructures becomes paramount. Potentially, more
complex core and shell geometries could also be fabricated and further
play an enhancing role. Multi-layer core-shell geometries include
insulating, semiconducting, or conductive materials that may improve the
electromagnetic response. Example materials that can be incorporated into
the multi-layers include, but are not limited to, metals, polymers, and
silicon dioxide. Long-range electromagnetic interactions as well as
two-dimensional and three-dimensional spatial relationships for isolated
nanostructures and junctions between nanostructures all can be optimized
in various embodiments. Electromagnetic enhancements at both the incident
and stokes-shifted wavelengths can be achieved by theory-driven
experimentation and optimization of the novel Raman nanostructure probes
and array platforms in some embodiments.

[0036] FIG. 3 shows the processing technique of IFM which allows for the
fabrication of an enhanced probe with a CNT base in a desired
configuration 30. According to one embodiment, FIG. 3(a) shows a CNT
probe with a single sharp bend 32. Similarly, FIG. 3(b) shows a CNT with
two sharp bends 34,

[0037] FIG. 3(c) shows a CNT with three sharp bends 36, and FIG. 3(d)
shows a CNT with four sharp bends 38. Each of these sharp bends operates
as a node for defining electromagnetic phenomena associated with the CNT.
Such electromagnetic phenomenon, as understood by a skilled person in the
art, enables the CNT to be used for a specified signal modification,
enhancement, transmission, and modulation.

[0038] FIG. 4 further illustrates different shapes and compositions of CNT
fabrication. In one embodiment, a composite nanostructure coated with a
noble metal (e.g., Pt, Au, Ag) can be fabricated in a variety of
nanoscale shapes. For example, the CNT can consist of a variable diameter
or a tapered angle. Similarly, the nanostructure can include an optional
oxide coating.

[0039] In one embodiment, a thin layer may also be added to the CNT to
improve adhesion between the CNT and a material. The adhesion of gold,
for example, is known to be weak on many different materials. The
addition of a thin adhesion layer, such as titanium, which is sandwiched
between the CNT and the gold, may be employed to minimize this problem.
The method of adhering additional/other materials to the CNT for improved
adhesion between the materials can be through a chemical reaction,
mechanical energy, heat, ion or electron bombardment or other methods.

[0040] Formation of the composite structure from the base CNT provides the
versatility to sequentially insulate and/or metallize the CNT, creating a
wide range of nanoscale shapes, dimensions and properties. Using IFM,
CNTs can be fabricated into a vertically-aligned or horizontally-aligned
CNT structure, or the CNT can be set at any angle that most strongly
interacts with the incident photons in a given instrumental layout.

[0042] The enhancement of the electric field at metal-dielectric
interfaces induced by illumination at optical frequencies is crucial for
Surface Enhanced Raman Scattering (SERS), and has enabled the detection
of single molecules. Metal dielectric interfaces support surface
electromagnetic waves known as surface plasmon polaritons. These optical
waves are essentially trapped at the interface because of their
interaction with the free electrons of the metal, leading to
highly-confined electromagnetic fields at the interface. Concentrating
light in this way leads to an electric field enhancement, which can be
used to boost nonlinear phenomena such as SERS.

[0043] To this regard, FIG. 5 illustrates SERS response of a silver-coated
CNT structure treated with 10-4M R6G, using 514 nm laser excitation
with a collection times of 10 and 100 seconds.

[0044] Atomic Force Microscopy (AFM) has played a role analyzing the
topography of surfaces but it has also played a well-known role in
highlighting Raman enhancement factors in TERS. In TERS, a metallized
sharp-tipped scanning probe is raster-scanned over a sample surface and
electromagnetic (EM) enhancement factors from the sharp tip increases the
Raman signal in a similar fashion to an isolated "rough" nanostructure as
in the SERS phenomena. According to one embodiment, the use of a probe on
a Scanning Probe Microscopy (SPM) platform and an array of the CNT probes
on a substrate results in one engineered nanostructure "in-hand" and an
array of the same, similar, or complimentary nanostructures on a
controlled surface and the potential to controllably create a "hot spot"
between the two or more nanostructures. Using an SPM platform, the single
probe can controllably be brought into precise proximity and relation to
any of the nanostructures or group configuration of nanostructures.
Optimal dimensions, physical and chemical properties, and spatial
relationships between neighboring nanostructures can be sought through
theoretical predictions and experiments to enhance the incident and
Stokes-shifted wavelengths. The near field region in the forward
direction from a nanoantenna creates a "hot spot" that arises from the
polarization and EM field enhancement from the nanoantenna. Advanced
nanoantenna geometries using nanomaterial processing capabilities,
combined with theory-led SPM experimentation makes this platform a
powerful tool as an advanced SERS/TERS substrate.

[0045] Embodiments Utilizing Raman Active Probes:

[0046] The single probe technology can be extended to fabrication of a
CNT-based Nanostructured Raman Sensor Array (NRSA) of varying density and
composition. These arrays provide a further opportunity to integrate CNT
fabrication with conventional silicon lithography, leading to
microdevices with precise nanoscale shape and aspect ratio control.
Refer, for example, to FIG. 6, illustrating a carbon nanotube based
molecular sensor system 60 consisting of a NRSA with highly-versatile
nanoengineered arrays of vertically aligned metal-coated carbon
nanotubes. Each array 62 consists of a plurality of CNT devices 64 formed
on a substrate. Those skilled in the art will readily extrapolate from
the description how to fabricate the NRSA. The CNTs may be formed in any
other arrangement as desired by the application or may be broken up into
smaller segments of CNT devices. The NSRA may be combined with material
and liquid handling capabilities or other combinations or improvements.

[0047] In the above illustration, the inter-carbon nanotube distance can
range from nanometers to microns. The length of exposed CNT can range
from 1 nm to 10 μm with the CNT diameter ranging from 1 nm to 40 nm.
Using thin film and electrochemical deposition techniques or other
techniques, the CNT can be controllably metallized and or insulated
modifying the nanostructure's Raman properties. The NRSA allows for
process control over inter-nanostructure distances, nanostructure size,
and aspect ratio maximizing the EM contribution to the Raman enhancement
and yielding a highly functional SERS substrate. The NRSA achieves
Emax per unit area and long-range EM interaction spacing within the
same nanoengineered substrate. The NRSA substrate, combined with the
single Raman enhanced probe, achieves Emax per unit volume by use of
a nanoengineered substrate in conjunction with an optimized TERS probe.
These probe and array properties and dimensions and the materials and
processes involved make the combined Raman enhancing probe and NRSA
substrate a powerful sensor system.

[0048] Other Commercial Embodiments

[0049] The same technology used to shape the Raman probes also can be
applied to arrays of CNTs. Combining the single molecule detection
capability of the proposed improved SERS AFM probe with an array of
aligned CNT structures opens up a wide variety of potential inexpensive
single molecule detection devices. One potential goal would be a device
equivalent to a computer hard drive with the readout head consisting of
the enhanced Raman CNT SERS probe, with a "compact disc (CD)" consisting
of aligned CNT structures, each chemically altered to selectively adsorb
or react with targeted analytes. The readout probe could very rapidly
address each individual CNT structure to determine the presence of a
particular analyte on a specific CNT within the array. The "CD" could be
a tiny mobile film or plate, and used for a wide variety of purposes. An
example includes using the "CD" as a monitor badge for chemical or
biological exposures or an explosive residue detector by reading the swab
of a surface. Another example is using the "CD" as a medical diagnostic
device or bioassay kit. The "CD" could then be inserted into the Raman
readout device.

[0050] The enhanced response in a localized region can be used for
purposes other than sensing. The enhancement mechanism can be used for
controllably modifying (chemically or otherwise) the surface of a
material in a localized region. The technology and methods described
herein can be further realized in useful functions, processes, or
techniques such as microlithography or nanolithography.

[0051] A Raman TERS readout device is another embodiment that allows
single molecule detection on each CNT structure. Such a CNT array device
with a TERS readout detector would offer a tremendously flexible, yet
extremely selective monitoring system. The CNT array TERS monitoring
system would offer the following capabilities:

[0053] 2) The array of CNTs gives a large number of densely-packed
activated sites providing the opportunity to simultaneously screen for a
wide variety of analytes.

[0054] 3) The chemical activation of the CNT structures and active areas
offer the opportunity to tailor the CNT monitor towards specific classes
of compounds or hazards.

[0055] 4) The Raman readout detector provides a final opportunity for
specificity and characterization.

[0056] Unless the context clearly requires otherwise, throughout the
description and the claims, the words "comprise," "comprising," and the
like are to be construed in an inclusive sense (i.e., to say, in the
sense of "including, but not limited to"), as opposed to an exclusive or
exhaustive sense. As used herein, the terms "connected," "coupled," or
any variant thereof means any connection or coupling, either direct or
indirect, between two or more elements. Such a coupling or connection
between the elements can be physical, logical, or a combination thereof.
Additionally, the words "herein," "above," "below," and words of similar
import, when used in this application, refer to this application as a
whole and not to any particular portions of this application. Where the
context permits, words in the above Detailed Description using the
singular or plural number may also include the plural or singular number
respectively. The word "or," in reference to a list of two or more items,
covers all of the following interpretations of the word: any of the items
in the list, all of the items in the list, and any combination of the
items in the list.

[0057] The above Detailed Description of examples of the invention is not
intended to be exhaustive or to limit the invention to the precise form
disclosed above. While specific examples for the invention are described
above for illustrative purposes, various equivalent modifications are
possible within the scope of the invention, as those skilled in the
relevant art will recognize. While processes or blocks are presented in a
given order in this application, alternative implementations may perform
routines having steps performed in a different order, or employ systems
having blocks in a different order. Some processes or blocks may be
deleted, moved, added, subdivided, combined, and/or modified to provide
alternative or subcombinations. Also, while processes or blocks are at
times shown as being performed in series, these processes or blocks may
instead be performed or implemented in parallel, or may be performed at
different times. Further any specific numbers noted herein are only
examples. It is understood that alternative implementations may employ
differing values or ranges.

[0058] The various illustrations and teachings provided herein can also be
applied to systems other than the system described above. The elements
and acts of the various examples described above can be combined to
provide further implementations of the invention.

[0059] Any patents and applications and other references noted above,
including any that may be listed in accompanying filing papers, are
incorporated herein by reference. Aspects of the invention can be
modified, if necessary, to employ the systems, functions, and concepts
included in such references to provide further implementations of the
invention.

[0060] These and other changes can be made to the invention in light of
the above Detailed Description. While the above description describes
certain examples of the invention, and describes the best mode
contemplated, no matter how detailed the above appears in text, the
invention can be practiced in many ways. Details of the system may vary
considerably in its specific implementation, while still being
encompassed by the invention disclosed herein. As noted above, particular
terminology used when describing certain features or aspects of the
invention should not be taken to imply that the terminology is being
redefined herein to be restricted to any specific characteristics,
features, or aspects of the invention with which that terminology is
associated. In general, the terms used in the following claims should not
be construed to limit the invention to the specific examples disclosed in
the specification, unless the above Detailed Description section
explicitly defines such terms. Accordingly, the actual scope of the
invention encompasses not only the disclosed examples, but also all
equivalent ways of practicing or implementing the invention under the
claims.